page_title: Traumatic insemination
section_title: Mechanics
hierarchical_section_title: Traumatic insemination / Mechanics
caption_attribution_description: The genitalia of the Callosobruchus analis beetle. It is covered in spines from base to tip. Referenced in Rönn, J., Katvala, M. &amp; Arnqvist, G. 2007. Coevolution between harmful male genitalia and female resistance in seed beetles. Proceedings of the National Academy of Sciences 104, 10921-1092. and Hotzy, C. &amp; Arnqvist, G. 2009. Sperm competition favors harmful males in seed beetles. Current Biology 19, 404-407.
context_page_description: Traumatic insemination, also known as hypodermic insemination, is the mating practice in some species of invertebrates in which the male pierces the female's abdomen with his aedeagus and injects his sperm through the wound into her abdominal cavity. The sperm diffuse through the female's hemolymph, reaching the ovaries and resulting in fertilization.
  The process is detrimental to the female's health. It creates an open wound which impairs the female until it heals, and is susceptible to infection. The injection of sperm and ejaculatory fluids into the hemocoel can also trigger an immune reaction in the female. Bed bugs, which reproduce solely by traumatic insemination, have evolved a pair of sperm-receptacles, known as the spermalege. It has been suggested that the spermalege reduces the direct damage to the female bed bug during traumatic insemination. However experiments found no conclusive evidence for that hypothesis; as of 2003, the preferred explanation for that organ is hygienic protection against bacteria.
  The evolutionary origins of traumatic insemination are disputed.
context_section_description: In humans and other vertebrates, blood and lymph circulate in two different systems, the circulatory system and lymphatic system, which are enclosed by systems of capillaries, veins, arteries, and nodes. This is known as a closed circulatory system. Insects, however, have an open circulatory system in which blood and lymph circulate unenclosed, and mix to form a substance called hemolymph. All organs of the insect are bathed in hemolymph, which provides oxygen and nutrients to all of the insect's organs.
  Following traumatic insemination, sperm can migrate through the hemolymph  to the female's ovaries, resulting in fertilization. The exact mechanics vary from taxon to taxon. In some orders of insects, the male genitalia (paramere) enters the female's genital tract, and a spine at its tip pierces the wall of the female's bursa copulatrix. In others, the male penetrates the outer body wall. In either case, following penetration, the male ejaculates into the female. The sperm and ejaculatory fluids diffuse through the female's hemolymph. The insemination is successful if the sperm reach the ovaries and fertilize an ovum.
  Female resistance to traumatic insemination varies from one species to another. Females from some genera, including Cimex, are passive prior to and during traumatic insemination. Females in other genera resist mating and attempt to escape. This resistance may not be an aversion to pain caused by the insemination, as observational evidence suggests that insects do not feel pain.
  Research into the paternity of offspring produced by traumatic insemination has found "significant" last-sperm precedence. That is, the last male to traumatically inseminate a female tends to sire most of the offspring from that female.
caption: The aedeagus of a Callosobruchus analis bean weevil. Some species of insect have evolved aedeagal spines, which damage the female reproductive tract. This has led to females using various techniques to resist being bred.
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